#include<bits/stdc++.h>
using namespace std;
int main()
{
	long long i,cnt=1,k,sum=0,day=1;
	cin>>k;
	while(day<=k)
	{
		for(i=1;i<=cnt&&day<=k;i++,day++)
			sum+=cnt;
		cnt++;
	}
	cout<<sum;
    return 0;
}
